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Storm water drainage

Storm water drainage

While flooding events might be unpredictable, city leaders recognize the growing number of such extreme weather events and are turning their attention to storm water drainage as an investment into the sustainably, resilience and livability of their city.

Related content

Flooding can devastate a city by compromising city services and destroying property and city assets. So while flooding events might be unpredictable, city leaders recognize the growing number of such extreme weather events and are now turning their attention to storm water drainage as an investment into the sustainably, resilience and livability of their city.

Defining the service

Storm water drainage services include the design, construction, maintenance, repair and operations of storm water collection and treatment systems, including everything from culverts and ditches through to sophisticated storm water treatment plants and reservoir systems.

Topline findings:

On average, cities spend US$0.62 per cubic meter of storm water drained.

The average city spends US$11,283 per kilometer of storm water network.

The vast majority of cities provide storm water drainage services to 100 percent of their properties.

Benchmarking analysis

Efficiency

Operating and capital cost per cubic meter of storm water drained. This measure combines the total storm water drainage operating costs with the total capital costs and divides the sum by the number of reported cubic meters of storm water drained.

Points to consider:

Storm water drainage, as a service is still emerging in many cities, largely because storm water was considered more of a nuisance than something deserving specific attention, creative solutions and financial commitment. Little wonder when we reached out to cities to see what services they might want to benchmark that this service popped up on our radar. Unfortunately when we asked for specific information necessary to calculate efficiency and effectiveness indicators, only six cities were able to respond.

There are two cities that appear to be outliers because of their low cost per cubic meter of storm water drained. City 1 and 23 show the cost per cubic meter of storm water drained at pennies on the dollar compared with US$1.98 for City 8. When we reviewed the outliers, we expect that the amount of storm water drained is the major reason for the low cost cities. We believe that these cities reported large quantities of storm water (denominator) and relatively small operating and capital costs. In other words, these are valid observations but certainly point to a concern that perhaps cities need to invest more and more in storm water drainage networks than they do today.

We experienced challenges in capturing the volume of storm water drained. Few cities actually measure the volume of storm water they collect. In part this is due to the fact that only recently are cities beginning to handle storm water in a manner similar to drinking water and wastewater. Recently cities have been introducing storm water drainage fees where the calculation may be either a flat rate charge or one that is determined by the percentage of a property that is non-permeable.

As cities experience more extreme weather events, regardless of their cause, they need to spend more on storm water drainage and seriously consider innovative ways in which to divert water, protect property, and prevent damage to valuable environmental features.

Operating and capital cost per cubic storm water drained (US$)

Effectiveness

Percent of properties served by storm water drainage service. This measure divides the number of properties directly connected to the storm water drainage network by the total number of properties that can be connected.

Points to consider:

Seven cities provided sufficient information to calculate this metric. With the exception of one city, all cities are effectively providing storm water drainage to properties in their city. The one city that only support 75 percent of the properties with this service may well be in the process of developing its storm water drainage network as a newer, more modern suburban municipality.

As cities begin to charge storm water drainage fees/charges, the likelihood of greater coverage and reduced storm water damage will improve.

Some cities are providing development credits or storm water drainage charge reductions when developers build special storm water holding tanks that mitigate large surface areas from contributing to large quantities of storm water, such as parking lots around shopping malls or multi-residential properties. Other credits deal with property owners that control the storm water quality so that “deleterious substances” do not make it into natural water courses. Residential property owners can use a variety of different techniques to control storm water flow, including: rain barrels, cisterns and infiltration galleries.

Future studies of storm water drainage may also include different techniques for calculating storm water drainage fees and/ or rebates on fees. Because this service aims to prevent flooding, future studies should examine the number of flooding incidents and/or the damage caused by floods. This information may need to be supplied by insurance companies who may/may not cover the costs of flood damage.

Frequency and severity of storm events — Capital requirements for maintenance and upgrades

Treatment and discharge requirements

Topography and ground cover/land use

More stringent regulatory requirements

New development costs

Innovative ideas

Supported by rebates from city council, more than 90,000 new domestic rainwater tanks were installed by Brisbane residents during the Millennium Drought event.

Authorities in Dresden have optimized their sewer system control to help better manage storm water during storm events.

In Mornington Peninsula, storm water authorities have implemented the Local Integrated Drainage Scheme (LIDS) to enhance and deliver flood mitigation works, and to reduce the risk of flooding to the population.

Toronto is considering a new storm water charge policy that would separate storm water services from water consumption in order to provide customers with greater fee transparency.

In neighboring Mississauga, authorities have introduced a credit program that provides financial recognition for private, on-site storm water measures that deliver direct benefits to the city’s storm water system.